DESCRIPTION

DSA_sign() computes a digital signature on the len byte message
digest dgst using the private key dsa and places its ASN.1 DER
encoding at sigret. The length of the signature is places in
*siglen. sigret must point to DSA_size(dsa) bytes of memory.

DSA_sign_setup() may be used to precompute part of the signing
operation in case signature generation is time-critical. It expects
dsa to contain DSA parameters. It places the precomputed values
in newly allocated BIGNUMs at *kinvp and *rp, after freeing
the old ones unless *kinvp and *rp are NULL. These values may
be passed to DSA_sign() in dsa->kinv and dsa->r.
ctx is a pre-allocated BN_CTX or NULL.

DSA_verify() verifies that the signature sigbuf of size siglen
matches a given message digest dgst of size len.
dsa is the signer's public key.

The type parameter is ignored.

The PRNG must be seeded before DSA_sign() (or DSA_sign_setup())
is called.

RETURN VALUES

DSA_sign() and DSA_sign_setup() return 1 on success, 0 on error.
DSA_verify() returns 1 for a valid signature, 0 for an incorrect
signature and -1 on error. The error codes can be obtained by
ERR_get_error(3).